Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2023		Jun. 30, 2022	Jun. 30, 2023		Jun. 30, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	$ 588		$ 467	$ 584	[1]	$ 447
Provision charged (credited) to income	18		63	30		94
Charge-offs	(5)		(1)	(16)		(20)
Recoveries	4		5	7		13
Net (charge-offs) recoveries	(1)		4	(9)		(7)
Allowance for credit losses - end of period	605	[1]	534	605	[1]	534
Commercial loans
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs				(6)
Commercial loans | Real Estate, including Construction
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	172		122	200		73
Provision charged (credited) to income	(26)		40	(54)		89
Charge-offs	0		0	0		0
Recoveries	0		0	0		0
Net (charge-offs) recoveries	0		0	0		0
Allowance for credit losses - end of period	146		162	146		162
Commercial loans | Business and corporate banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	264		197	230		243
Provision charged (credited) to income	31		22	69		(18)
Charge-offs	(1)		(1)	(6)		(9)
Recoveries	1		0	2		2
Net (charge-offs) recoveries	0		(1)	(4)		(7)
Allowance for credit losses - end of period	295		218	295		218
Commercial loans | Global banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	132		120	120		100
Provision charged (credited) to income	19		(2)	31		27
Charge-offs	0		0	0		(9)
Recoveries	0		0	0		0
Net (charge-offs) recoveries	0		0	0		(9)
Allowance for credit losses - end of period	151		118	151		118
Commercial loans | Other commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	1		2	1		4
Provision charged (credited) to income	0		(1)	0		(3)
Charge-offs	0		0	0		0
Recoveries	0		0	0		0
Net (charge-offs) recoveries	0		0	0		0
Allowance for credit losses - end of period	1		1	1		1
Consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs				(10)
Consumer loans | Residential Mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	(2)		5	11		8
Provision charged (credited) to income	(12)		(1)	(22)		(5)
Charge-offs	(1)		0	(4)		(1)
Recoveries	2		2	2		4
Net (charge-offs) recoveries	1		2	(2)		3
Allowance for credit losses - end of period	(13)		6	(13)		6
Consumer loans | Home equity mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	3		6	2		5
Provision charged (credited) to income	4		1	5		1
Charge-offs	0		0	(1)		(1)
Recoveries	0		0	1		2
Net (charge-offs) recoveries	0		0	0		1
Allowance for credit losses - end of period	7		7	7		7
Consumer loans | Credit cards
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	15		15	16		14
Provision charged (credited) to income	1		5	1		4
Charge-offs	(2)		0	(4)		0
Recoveries	1		2	2		4
Net (charge-offs) recoveries	(1)		2	(2)		4
Allowance for credit losses - end of period	15		22	15		22
Consumer loans | Other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	3		0	4		0
Provision charged (credited) to income	1		(1)	0		(1)
Charge-offs	(1)		0	(1)		0
Recoveries	0		1	0		1
Net (charge-offs) recoveries	(1)		1	(1)		1
Allowance for credit losses - end of period	$ 3		$ 0	$ 3		$ 0

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at June 30, 2023 and December 31, 2022. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 17, "Variable Interest Entities," for additional information. June 30, 2023December 31, 2022(in millions)AssetsLoans, net$186 $162 Other assets40 44 Total assets$226 $206 LiabilitiesInterest, taxes and other liabilities$35 $22 Total liabilities$35 $22